US Democratic presidential candidates Hillary Clinton (R) and Bernie Sanders shake hands as they participate in the MSNBC Democratic Candidates Debate at the University of New Hampshire in Durham on February 4, 2016.
Clinton and Sanders face off on February 4, in the first debate since their bruising Iowa clash that the former secretary of state won by a hair, as they gear for a battle royale in New Hampshire. / AFP / Jewel Samad (Photo credit should read JEWEL SAMAD/AFP/Getty Images)

US Democratic presidential candidate Bernie Sanders participates in the MSNBC Democratic Candidates Debate at the University of New Hampshire in Durham on February 4, 2016.
Clinton and Sanders face off on February 4, in the first debate since their bruising Iowa clash that the former secretary of state won by a hair, as they gear for a battle royale in New Hampshire. / AFP / Jewel Samad / ALTERNATE CROP (Photo credit should read JEWEL SAMAD/AFP/Getty Images)

US Democratic presidential candidates Hillary Clinton arrives on stage before participating in the MSNBC Democratic Candidates Debate at the University of New Hampshire in Durham on February 4, 2016.
Clinton and Sanders face off on February 4, in the first debate since their bruising Iowa clash that the former secretary of state won by a hair, as they gear for a battle royale in New Hampshire. / AFP / JEWEL SAMAD / ALTERNATE CROP (Photo credit should read JEWEL SAMAD/AFP/Getty Images)

EDITORS NOTE: Graphic content / US Democratic presidential candidates Hillary Clinton (R) and Bernie Sanders chat during a break as they participate in the MSNBC Democratic Candidates Debate at the University of New Hampshire in Durham on February 4, 2016.
Clinton and Sanders face off on February 4, in the first debate since their bruising Iowa clash that the former secretary of state won by a hair, as they gear for a battle royale in New Hampshire. / AFP / Jewel Samad (Photo credit should read JEWEL SAMAD/AFP/Getty Images)

EDITORS NOTE: Graphic content / US Democratic presidential candidate Bernie Sanders leaves the stage during a break as he participate in the MSNBC Democratic Candidates Debate with Hillary Clinton at the University of New Hampshire in Durham on February 4, 2016.
Clinton and Sanders face off on February 4, in the first debate since their bruising Iowa clash that the former secretary of state won by a hair, as they gear for a battle royale in New Hampshire. / AFP / Jewel Samad (Photo credit should read JEWEL SAMAD/AFP/Getty Images)

EDITORS NOTE: Graphic content / US Democratic presidential candidates Hillary Clinton (R) and Bernie Sanders participate in the MSNBC Democratic Candidates Debate at the University of New Hampshire in Durham on February 4, 2016.
Clinton and Sanders face off on February 4, in the first debate since their bruising Iowa clash that the former secretary of state won by a hair, as they gear for a battle royale in New Hampshire. / AFP / Jewel Samad (Photo credit should read JEWEL SAMAD/AFP/Getty Images)

EDITORS NOTE: Graphic content / US Democratic presidential candidate Hillary Clinton participates in the MSNBC Democratic Candidates Debate with Bernie Sanders at the University of New Hampshire in Durham on February 4, 2016.
Clinton and Sanders face off on February 4, in the first debate since their bruising Iowa clash that the former secretary of state won by a hair, as they gear for a battle royale in New Hampshire. / AFP / Jewel Samad (Photo credit should read JEWEL SAMAD/AFP/Getty Images)

DURHAM, NH - FEBRUARY 04: Democratic presidential candidate former Secretary of State Hillary Clinton and U.S. Sen. Bernie Sanders (I-VT) shake hands at the start of their MSNBC Democratic Candidates Debate at the University of New Hampshire on February 4, 2016 in Durham, New Hampshire. This is the final debate for the Democratic candidates before the New Hampshire primaries.Ã (Photo by Joe Raedle/Getty Images)

DURHAM, NH - FEBRUARY 04: The stage is set for the start of the MSNBC Democratic Candidates Debate at the University of New Hampshire on February 4, 2016. Democratic and Republican Presidential candidates are stumping for votes throughout New Hampshire leading up to the primary on February 9. (Photo by Joe Raedle/Getty Images)

DURHAM, NH - FEBRUARY 04: Democratic presidential candidate former Secretary of State Hillary Clinton and U.S. Sen. Bernie Sanders (I-VT) stand next to each other at the start of their MSNBC Democratic Candidates Debate at the University of New Hampshire on February 4, 2016 in Durham, New Hampshire. This is the final debate for the Democratic candidates before the New Hampshire primaries.Ã (Photo by Joe Raedle/Getty Images)

DURHAM, NH - FEBRUARY 04: Democratic presidential candidate former Secretary of State Hillary Clinton and U.S. Sen. Bernie Sanders (I-VT) stand next to each other at the start of their MSNBC Democratic Candidates Debate at the University of New Hampshire on February 4, 2016 in Durham, New Hampshire. This is the final debate for the Democratic candidates before the New Hampshire primaries.Ã (Photo by Joe Raedle/Getty Images)

EDITORS NOTE: Graphic content / US Democratic presidential candidates Hillary Clinton (R) and Bernie Sanders participate in the MSNBC Democratic Candidates Debate at the University of New Hampshire in Durham on February 4, 2016.
Clinton and Sanders face off on February 4, in the first debate since their bruising Iowa clash that the former secretary of state won by a hair, as they gear for a battle royale in New Hampshire. / AFP / Jewel Samad (Photo credit should read JEWEL SAMAD/AFP/Getty Images)

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She went on to say that it was beneath Sanders' dignity to raise such doubts about her:

Which really comes down to: Anybody who ever took donations or speaking fees from any interest group has to be bought. And I just absolutely reject that, senator. And I really don't think these kinds of attacks by insinuation are worthy of you. And enough is enough.

If you've got something to say, say it directly. But you will not find that I ever changed a view or a vote because of any donation that I ever received. ... I think it's time to end the very artful smear that you and your campaign have been carrying out in recent weeks.

Sanders responded by arguing that corporate money and lobbying exert influence over elected officials.

Sanders said:

Let's talk about why in the 1990s, Wall Street got deregulated. Did it have anything to do with the fact that Wall Street spent billions of dollars on lobbying and campaign contributions? Well, some people might think, some people might think, "Yeah, that may have some influence.

He added:

There is a reason why these people are putting huge amounts of money into our political system. In my view, it is undermining American democracy, and it is allowing Congress to represent wealthy campaign contributors and not the working families of this country.

Clinton has struggled to address her speaking fees in the past, including during a town-hall event on Wednesday night, in which she was pressed about receiving hundreds of thousands of dollars from the investment bank Goldman Sachs.